Bacterial canker of stone‐fruits: Infection experiments with <i>Pseudomonas mors‐prunorum</i> and <i>P. syringae</i>

Abstract

SUMMARY The effect was compared of inoculating Pseudomonas mors‐prunorum and P. syringae at high inoculum concentration through wounds in plum stems and cherry branches, and through cherry‐leaf scars. In the wound inoculations a North American cherry strain of P. syringae was considerably more virulent than any of three indigenous cherry strains of P. mors‐prunorum , but two pear strains of P. syringae were less virulent. P. mors‐prunorum showed a much greater capacity to invade through leaf scars, particularly towards the end of the leaf‐fall period, when all three P. syringae strains were largely ineffective. Evidence is discussed which suggests that the greater infectivity of the P. mors‐prunorum strains through leaf scars was related to their capacity to colonize the host tissues from small inocula. The P. syringae strains died out in cherry cankers earlier than P. mors‐prunorum strains and they were less stable during host passage. The results of the experiments indicate that virulence in these organisms is a complex phenomenon and determined by several factors.